This invention relates generally to bearing systems and more particularly to ball bearing systems.
Ball bearings are widely used where one part must rotate relative to another part. Ball bearing assemblies are commercially available.
These assemblies contain an outer ring and an inner ring. The inside of the outer ring and the outside of the inner ring are grooved. The grooves are aligned to form a raceway to contain metal balls. The two rings "roll" on the balls and are free to rotate relative to each other. In use, the inner ring is often mounted to a shaft. The outer ring is mounted to some base. The shaft is thus free to rotate relative to the base.
Commercially available ball bearing assemblies will withstand a specified range of axial and radial forces on the shaft. If forces in excess of the specified range are applied to the shaft, the bearing assembly may fail. For example, the balls or the races might become permanently deformed such that the balls no longer roll smoothly in the races. Alternatively, the balls or races might fracture.
One method of lessening failures associated with forces along the shaft is to use several bearings. For example, using four ball bearings on a shaft instead of two allows twice as much force to be applied to the shaft before the ball bearings fail.
The ability of the ball bearings to withstand forces without failing can also be increased by increasing the size of the bearings or the number of balls in each ball bearing.
While these known techniques can increase resistance to forces on the shaft, they also add manufacturing complexity, cost, size, and weight. The known techniques for making bearing assemblies which can withstand high forces also have more friction than a simple assembly. Since higher friction requires more power to turn the shaft, the known techniques may not be adequate for some applications. In a class of modern military projectiles, called "smart munitions", these limitations can be very significant. For example, when the projectile is fired, very large forces are applied to the shaft. Thereafter, a seeker head mounted on the shaft must spin very smoothly in order to guide the projectile. Since the projectile explodes at the end of its flight, the cost of the projectile must be minimized. Also, size and weight impact the performance of the projectile.